With no dedicated hydrodynamical simulations of magnetospheric accretion onto planets,
we take as rough guidance the values for the filling factor inferred for CTTSs.
In the sample by [1]}, \(\approx 80~\%\)  of the stars
have an estimated global \(f_{\mathrm {fill}}< 10~\%\) ,
and often amounting to a few percents or fractions of a percent.
The same order-of-magnitude estimates have been reported in [2]},
with there \(f_{\mathrm {fill}}\)  typically less than 10 %, using spectroscopic data.
More recently, [3]} similarly found filling factors of tens of percent for a few objects from HST low-resolution observations.
Estimates derived from multi-wavelength time-series photometry can be less precise,
but they also indicate typically \(f_{\mathrm {fill}}<10~\%\) –20 % for the bulk of CTTSs
dominated by hot accretion spots (e.g. [4]}, [5]}, [6]}).
